1. Field of the Invention
The present invention relates to replaceable filter elements. Specifically, the present invention relates to a drop in, inside-out flow replaceable filter element with shielded bottom bypass valve.
2. Background Information
Industrial fluids are critical in many industrial machines and include hydraulic fluids, lubricating fluids, cooling fluids, liquid fuels and others. The phrase industrial fluid is intended to be comprehensive of these fluids and others and is equivalent to the term working fluid herein. In many of these applications the industrial fluid is in a circulating system. For example, hydraulic fluids are typically found in a circulating hydraulic system, wherein such systems are frequently used in heavy machinery, including cranes, backhoes, demolition shears, bulldozers, and the like. In such circulating hydraulic systems, it is important to keep the hydraulic fluid free of debris. Consequently, filter units or filter assemblies have been incorporated in the hydraulic systems to filter debris from the hydraulic fluid. Lubricating fluid, e.g. oil, will be found in circulating lubrication systems, wherein such systems have also incorporated filter assemblies to clean the working fluid. Fuel systems utilizing liquid fuels have also incorporated filter assemblies to clean the fuel, however the fuel systems do not, typically, re-circulate the working fluid. The phrase circulating industrial fluid or circulating working fluid is intended to be comprehensive of industrial fluids in a circulating system.
It is common to form the filter assembly with a replaceable filter element. One common configuration is a tubular filter media in which the fluid being cleaned flows in a radial direction through the tubular pleated media. The direction of flow in such a structure defines the filter element as an outside-in (flow of fluid being cleaned is inward radial direction) or an inside-out (flow of fluid being cleaned is outward radial direction) filter structure. Examples of the tubular structure type filter elements include the K series element sold by Schroeder Industries, LLC, with the direction of flow for this element being defined by the associated assembly.
From an operational standpoint there are certain advantages to outside-in flow and other advantages with inside-out flow. Namely with outside-in flow the pleat structure can be more stable at higher pressure when constructed with a traditional fan pleat. This structure also exhibits higher dirt holding capacity as compared to similar inside out designs, since the media pleats are uniformly exposed to the system flow which results in a more uniform distributed deposition pattern. See, for example, an outside in flow design filter described in the Assignee's U.S. Pat. No. 7,384,547 entitled “Replaceable Filter Element with Integral Annular Trap” which is incorporated herein by reference. An inside out flow design is shown in U.S. Pat. No. 4,428,834. Numerous other patents illustrate inside out and outside in flow designs.
Alternatively with inside-out flow there is an advantage in that trapped particles on the up-stream side of the filter remain in the center and are easily removed with the filter element, whereas in the outside in configurations such particles can, in theory, contaminate the system by falling or migrating past the filter location during filter element replacement.
The associated mounting structure of the filter element in the filter assembly housing will often differ between the inside out flow and the outside in flow designs. The inside out flow design is common where the filter element is a drop-in design that has the end cap on the inlet side engage the housing to support the element. This is sometimes called a vertical hanging element, although in many applications, such as vehicles, the filter element will not maintain a single vertical orientation as the housing moves with the vehicle.
Many if not most industrial fluid systems that utilize a filter assembly require a bypass valve to be associated with the filter assembly. The purpose of the bypass valve is to allow the working fluid to bypass the filter assembly in certain critical situations. In general, the bypass opens if the pressure drop becomes too large across the filter assembly, i.e. above a set operating pressure of the bypass valve. The bypass operation, i.e. working fluid moving through the open bypass valve and bypassing the filter media, is not the standard operating condition of such filter assemblies and, when triggered, can be an indication that the filter element is in need of replacement. For example as the pleated media of a filter element becomes clogged then the pressure drop across the media increases causing the bypass valve to move to the open position. Further, bypass operation may also be triggered with the starting of a system, also known as cold starts, where the pressure gradient across the filter element exceeds the bypass valve threshold at the start (and then closes with the movement of fluid). One conventional bypass valve configuration is a spring biased poppet valve.
It is known in the art, and even common, to incorporate bypass valves into replaceable filter elements. In a drop in type, inside out flow replaceable filter element it has been known to incorporate a bypass valve in the lower end cap structure. Although a very convenient bypass valve placement for not interfering with other flow aspects of the filter assembly, this configuration has lead to certain contamination issues. As noted above, in the inside out flow elements particulate material that is filtered out of the working fluid by the filter media remains on the inside of the filter element structure in the normal operation of the filter element. This particulate material can and does become dislodged from the filter media and then settles to the bottom of the filter element, effectively covering (even caking) the bypass valve structure. With the operation of the bypass valve the (previously filtered) particulate material can move through the open bypass valve and contaminate the system. The problem can become more concerning where the bypass valve operates at times other than near the end of the useful life of the filter element, such as cold starts as noted above.
In cold starts of some systems, the working fluid is cool or cold and exhibits higher viscosity than at normal operating temperatures which results in higher differential pressure drop through filter elements. During this common situation, the pressure drop may be great enough to cause the bypass valve to open until the system begins flowing and normal operation commences. Contamination that settles on or in the vicinity of the bypass valve opening are flushed through the bypass valve when it opens and migrates downstream of the filter assembly. When such events occur, large amounts of previously filtered contamination may be released into the working fluid which endangers sensitive system components.
There remains a need to improve the operation of inside out flow, drop in type filter elements having integrated lower bypass valves to minimize the ability of dislodged filter particulates from moving beyond the filter element and re-entering the system.